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Wednesday, March 11, 2026

SolderSmoke Direct Conversion Receiver: TOROIDS! Steve N7PHR's Handouts on the BP Filter and the Mixer/Diplexer

 



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Winding the trifilar toroids was the hardest part of building the mixer board, and with the high school students, I admit to chickening out.   Instead I prepared about 17 of them using a batch from Hyderabad (wound by the seamstresses!) that Farhan left me.  Here is  how we did it: https://soldersmoke.blogspot.com/2023/02/progress-report-high-school-students_25.html Steve's use of wires of different colors is a good idea.  It helps to keep track of the different wires.  

We often hear that winding toroids is a show-stopper for many would-be homebrewers.  This should not be the case.   Winding the coils is not difficult.  

The Diplexer came from Roy Lewellan W7EL's optimized QRP Transceiver.  Dean and I were struggling with the suppression of signal from Radio Marti on 7335 kHz.  When we added Roy's diplexer, it seemed to help knock down Radio Marti.  

We too used the NanoVNA to tune the BP filter.  I remember this as one of the more pleasing moments for the students. 

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